Communication apparatus and transmission method for transmitting a demodulation reference signal

ABSTRACT

A repetition unit (212) performs a repetition for mapping a data signal and a demodulation reference signal (DMRS) repeatedly at a symbol level over a plurality of subframes. A signal allocation unit (213) maps, in the a plurality of subframes, the repeated DMRS to symbols other than symbols corresponding to an SRS resource candidate, which is a candidate for a resource to which a sounding reference signal (SRS) to be used to measure an uplink received signal quality is to be mapped. A transmission unit (216) transmits an uplink signal (PUSCH) including the DMRS and the data signal over the a plurality of subframes.

TECHNICAL FIELD

The present disclosure relates to a terminal and a transmission method.

BACKGROUND ART

In recent years, a promising mechanism for supporting the futureinformation society is machine-to-machine (M2M) communication, whichrealizes a service by autonomous communication between machines, withoutinvolving user judgment. A smart grid is an example of a specificapplied case of an M2M system. A smart grid is an infrastructure systemthat efficiently supplies a lifeline such as electricity or gas. Forexample, on a smart grid, M2M communication is performed between smartmeters installed in each home or each building, and a central server,and the demand balance of resources is adjusted autonomously andefficiently. Other examples of an applied case of an M2M communicationsystem include monitoring systems for product management, environmentsensing, telemedicine, and the like, remote management of the stockingand charging of vending machines, and the like.

In M2M communication systems, the use of cellular systems having aparticularly wide communication area is being focused on. In 3GPP, anM2M-focused cellular network advancement called NarrowBand Internet ofThings (NB-IoT) is being standardized (for example, see NPL 4), and thespecifications are being considered to meet the demands of lower-costterminals, reduced power consumption, and coverage enhancement. Inparticularly, unlike handset terminals which are often used by userswhile moving, for terminals such as smart meters with little to nomotion, securing coverage is an absolutely necessary condition forproviding a service. For this reason, to accommodate the case in which aterminal is disposed in a location which is unusable in thecommunication areas of existing cellular networks (for example, LTE andLTE-Advanced), such as the basement of a building, coverage enhancementto further expand the communication area is an important issue underconsideration.

Whereas existing LTE resource blocks are made up of 12 subcarriers, toexpand the communication area while reducing power consumption of theterminal (hereinafter also called an NB-IoT terminal), the NB-IoT uplinksupports transmission on numbers of subcarriers which are less than 12(for example, 1, 3, and 6 subcarriers). By having a terminal transmit onfewer subcarriers (in other words, transmit on a narrower band), thepower spectral density increases, thereby improving the receiversensitivity and expanding coverage.

In the case in which a terminal transmits on a number of subcarriersless than 12 subcarriers, if resources are allocated to the terminalevery 1 subframe, which is the existing unit of time for LTE resourceblocks, the number of resource elements (REs) which may be allocated tothe terminal at one time is reduced. For example, supposing the PUSCH ofexisting LTE as illustrated in FIG. 1 , in the case in which theterminal transmits on 12 subcarriers, 12 (SC-FDMA symbols)×12(subcarriers)=144 REs may be allocated for data transmission. On theother hand, in the case in which the terminal transmits on 1subcarriers, 12 (SC-FDMA symbols)×1 (subcarrier)=12 REs are allocatedfor data transmission. In the case in which data with the same transportblock size is transmitted, the code rate increases with fewer REs. Also,to maintain the same code rate, it is necessary to reduce the transportblock size, but overhead such as header information and the cyclicredundancy check (CRC) becomes larger with respect to the data size.

In NB-IoT, to keep the number of REs which may be allocated to aterminal at one time to the same degree as the existing LTE, the numberof allocable subframes is increased in accordance with the number oftransmission subcarriers. For example, the units of resources toallocate at one time (hereinafter designated scheduling units orresource units) are taken to be 8 subframes in the case of a terminaltransmitting on 1 subcarrier, 4 subframes in the case of a terminaltransmitting on 3 subcarriers, and 2 subframes in the case of a terminaltransmitting on 6 subcarriers.

In NB-IoT, coverage enhancement of up to approximately 20 dB compared toan LTE communication area is demanded. In transmission on fewer than 12subcarriers as described above, for example, in the case of a terminaltransmitting on M subcarriers, a coverage improvement of 10 log₁₀(12/M)dB compared to the case of transmitting on 12 subcarriers is anticipatedtheoretically. For example, in the case of 1 subcarrier transmission,the coverage may be improved by up to approximately 11 dB compared toLTE transmission on 12 subcarriers. However, to realize the 20 dBcoverage improvement demanded by NB-IoT, in addition to 1 subcarriertransmission, the application of additional coverage-improvingtechnology is essential.

Accordingly, to enhance coverage, the introduction of repetitiontechnology, which repeatedly transmits the same signal on thetransmitting side, and combines the signals on the receiving side toimprove the receiver sensitivity and enhance coverage, is beingconsidered.

Furthermore, the NB-IoT terminals needing coverage enhancement havelittle to no motion, and by focusing on the supposition of anenvironment without channel variation over time, the use of technologyfor improving the channel estimation accuracy is also being considered.

One example of technology for improving the channel estimation accuracyis “a plurality of subframe channel estimation and symbol levelcombining” (for example, see NPL 5). With a plurality of subframechannel estimation and symbol level combining, as illustrated in FIG. 4, for a signal transmitted by repetition over a plurality of subframes(R subframes), the base station performs coherent combining at thesymbol level over a number of subframes equal to the number ofrepetitions or a number of subframes less than the number of repetitions(X subframes). After that, the base station performs channel estimationusing the coherently combined DMRS, and uses the obtained channelestimation result to perform demodulation/decoding of the SC-FDMA datasymbols.

In the case in which the units for performing a plurality of subframechannel estimation and symbol level combining, namely the number ofsubframes (X), is less than the number of repetitions (R), the basestation combines (R/X) symbols after demodulation and decoding.

By using a plurality of subframe channel estimation and symbol levelcombining, the PUSCH transmission quality may be improved compared tosimple repetition that performs channel estimation and thedemodulation/decoding of SC-FDMA data symbols at the subframe level (forexample, see NPL 5).

CITATION LIST Non Patent Literature

NPL 1: 3GPP TS 36.211 V13.0.0, “Evolved Universal Terrestrial RadioAccess (E-UTRA); Physical channels and modulation (Release 13),”December 2015.

NPL 2: 3GPP TS 36.212 V13.0.0, “Evolved Universal Terrestrial RadioAccess (E-UTRA); Multiplexing and channel coding (Release 13),” December2015.

NPL 3: 3GPP TS 36.213 V13.0.0, “Evolved Universal Terrestrial RadioAccess (E-UTRA); Physical layer procedures (Release 13),” December 2015.

NPL 4: RP-151621, Qualcomm, “New Work Item: NarrowBand IOT (NB-IOT)”

NPL 5: R1-150312, Panasonic, “Discussion and performance evaluation onPUSCH coverage enhancement”

NPL 6: R1-151587, Samsung, “Considerations of legacy SRS impact onuplink transmission from low-cost UE,” April 2015

NPL 7: R1-152703, LG Electronics, “Discussion on PUSCH transmission forMTC,” May 2015

SUMMARY OF INVENTION

In a cell that supports NB-IoT terminals, it is necessary to accommodatethe coexistence of NB-IoT terminals and existing LTE terminals, and itis desirable to improve the transmission quality for NB-IoT terminalswhile minimizing the impact on the existing LTE system.

An aspect of the present disclosure provides a terminal and atransmission method capable of improving the transmission quality forNB-IoT terminals while minimizing the impact on an existing LTE system.

A terminal according to an aspect of the present disclosure adopts aconfiguration including: a repetition unit that performs a repetitionfor mapping a data signal and a demodulation reference signal (DMRS)repeatedly at a symbol level over a plurality of subframes; a signalallocation unit that maps, in the a plurality of subframes, the repeatedDMRS to symbols other than symbols corresponding to an SRS resourcecandidate, which is a candidate for a resource to which a soundingreference signal (SRS) used to measure an uplink received signal qualityis to be mapped; and a transmission unit that transmits an uplink signalincluding the DMRS and the data signal in the a plurality of subframes.

It should be noted that general or specific embodiments may beimplemented as a system, a method, an integrated circuit, a computerprogram, a storage medium, or any selective combination thereof.

According to an aspect of the present disclosure, it is possible toimprove the transmission quality for NB-IoT terminals while minimizingthe impact on an existing LTE system.

Additional benefits and advantages according to an aspect of the presentdisclosure will become apparent from the specification and the drawings.The benefits and/or advantages may be individually obtained by thevarious embodiments and features of the specification and drawings,which need not all be provided in order to obtain one or more of suchbenefits and/or advantages.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating an example of a PUSCH subframeconfiguration.

FIG. 2 is a diagram illustrating an example of an srs-SubframeConfigdefinition.

FIG. 3 is a diagram illustrating an exemplary setting of SRStransmission candidate subframes and SRS resources.

FIG. 4 is a diagram illustrating exemplary operations of a plurality ofsubframe channel estimation and symbol level combining.

FIG. 5 is a diagram illustrating exemplary operations of repetition atthe resource unit level.

FIG. 6 is a diagram illustrating exemplary operations of repetition atthe subframe level.

FIG. 7 is a diagram illustrating exemplary operations of repetition atthe symbol level.

FIG. 8 is a block diagram illustrating a principal configuration of aterminal according to Embodiment 1.

FIG. 9 is a block diagram illustrating a configuration of a base stationaccording to Embodiment 1.

FIG. 10 is a block diagram illustrating a configuration of the terminalaccording to Embodiment 1.

FIG. 11 is a diagram illustrating exemplary operations of PUSCHrepetition transmission according to Embodiment 1.

FIG. 12 is a diagram illustrating exemplary operations of PUSCHrepetition transmission according to Embodiment 2.

FIG. 13 is a diagram illustrating exemplary operations of PUSCHrepetition transmission according to Embodiment 3.

DESCRIPTION OF EMBODIMENTS

[SRS Resource Candidates in LTE]

First, resource candidates in LTE will be described.

In 3rd Generation Partnership Project Long Term Evolution (3GPP LTE),orthogonal frequency-division multiple access (OFDMA) is adopted as thedownlink communication method from a base station (also called an eNB)to a terminal (user equipment (UE)), while single-carrierfrequency-division multiple access (SC-FDMA) is adopted as the uplinkcommunication method from a terminal to a base station (for example, seeNPL 1 to 3).

In LTE, communication is performed by having the base station allocateresource blocks (RBs) inside the system band to terminals per a unit oftime called a subframe. FIG. 1 illustrates an exemplary configuration ofa subframe in the physical uplink shared channel (PUSCH) of LTE. Asillustrated in FIG. 1 , a single subframe contains two time slots. Ineach slot, a plurality of SC-FDMA data symbols and a demodulationreference signal (DMRS) are time-multiplexed. The base station receivesthe PUSCH, and uses the DMRS to perform channel estimation. After that,the base station uses the channel estimation result to performdemodulation/decoding of the SC-FDMA data symbols.

Also, on the LTE uplink, for measure the received signal quality betweenthe base station and the terminal, a sounding reference signal (SRS) isused (for example, see NPL 1, 3). The SRS is mapped to SRS resources,and transmitted from the terminal to the base station. Herein, by acell-specific higher-layer indication, the base station sets an SRSresource candidate group that includes SRS resource candidates sharedamong all terminals existing inside the target cell. After that, by aterminal-specific higher-layer indication, SRS resources in a subset ofthe SRS resource candidate group are allocated to each terminal to beallocated with SRS resources. A terminal maps the SRS to the allocatedSRS resources, and transmits to the base station. Note that each SRSresource candidate is the last symbol in a subframe acting as an SRStransmission candidate (SRS transmission candidate subframe). Also, withregard to the symbols that act as SRS resource candidates, no terminalsinside the cell in which the SRS resource candidate group is set performdata transmission, thereby preventing collisions between the SRS and adata signal (PUSCH signal).

In LTE, srs-SubframeConfig and the like is defined as a cell-specifichigher-layer indication that sets the SRS resource candidate group (forexample, see NPL 1). FIG. 2 illustrates an example of srs-SubframeConfigdefinitions. One of the srs-SubframeConfig numbers (from 0 to 15)illustrated in FIG. 2 is transmitted from the base station to theterminal. With this arrangement, a transmission interval (T_(SFC)) atwhich to transmit the SRS and an offset (Δ_(SFC)) for indicating thesubframe in which to start transmission of the SRS are indicated fromthe base station to the terminal. For example, in FIG. 2 , in the casein which the srs-SubframeConfig number is 4 (Binary=0100), thetransmission interval T_(SFC)=5, and the offset Δ_(SFC)=1. In this case,the 2nd (=1+Δ_(SFC)), the 7th (=1+Δ_(SFC)+(T_(SFC)×1)), the 12th(=1+Δ_(SFC)+(T_(SFC)×2)), and so on to the nth (1+Δ_(SFC)+(T_(SFC)×n))subframes become SRS transmission candidate subframes (for example, seeFIG. 3 ).

BACKGROUND LEADING UP TO PRESENT DISCLOSURE

Next, the background leading up to the present disclosure will bedescribed.

As described above, in NB-IoT, a terminal transmits on a number ofsubcarriers less than 12 subcarriers and in a number of subframesgreater than 1 subframe as a single resource allocation unit (resourceunit). Furthermore, to improve coverage, repetition for repeatedlytransmitting the same signal a plurality of times is applied. In otherwords, in the time domain, provided that X is the number of subframesper resource unit, and R is the number of repetitions, (X×R) subframesare used for transmission.

As for the method of repeating resource units a plurality of times, thethree methods indicated below are conceivable.

The first is repetition at the resource unit level. FIG. 5 illustratesan example of repetition at the resource unit level (the case of X=8 andR=4).

The second is repetition at the subframe level. With repetition at thesubframe level, the terminal transmits a subframe signal including thesame signal inside the resource unit in consecutive subframes. FIG. 6illustrates an example of repetition at the subframe level (the case ofX=8 and R=4). With repetition at the subframe level, since a subframesignal including the same signal is transmitted in consecutivesubframes, compared to repetition at the resource unit level, signalsare less susceptible to frequency error, and the symbol level combiningdescribed above is easy to apply.

The third is repetition at the symbol level. With repetition at thesymbol level, the terminal transmits single-carrier frequency-divisionmultiple access (SC-FDMA) symbols including the same signal inside theresource unit in consecutive symbols. FIG. 7 illustrates an example ofrepetition at the symbol level (the case of X=1 and R=4). Note that inFIG. 7 and the following description, for the sake of simplicity, thecase in which the number of subframes per resource unit is X=1 isillustrated as an example. With repetition at the symbol level, sincesymbols including the same signal are transmitted consecutively,compared to repetition at the subframe level, signals are even lesssusceptible to frequency error, and the effect of coverage improvementdue to symbol level combining is greater.

Meanwhile, in NB-IoT, three operating modes are prescribed, namely a“Standalone mode” that uses the Global System for Mobile communications(GSM®) frequency band, a “Guard-band mode” that uses an unused frequencyband provided to prevent interference with a separate system utilizingan adjacent frequency band in LTE, and an “In-band mode” that uses aportion of the existing LTE frequency band.

In the In-band mode, in a cell that supports NB-IoT terminals, it isnecessary to accommodate the coexistence of existing LTE terminals andNB-IoT terminals, and it is desirable to support NB-IoT terminals so asto minimize the impact on the existing LTE system. For this reason, inthe uplink transmission of NB-IoT terminals, it is necessary to preventcollisions with the SRS, which has the possibility of being transmittedover the entire system band by existing LTE terminals.

In the PUSCH transmission of an LTE system, the following two methodsexist as the format by which an LTE terminal transmits data in an SRStransmission candidate subframe. The first method is a method thatpunctures the last symbol after mapping data to 12 SC-FDMA symbolsexcluding the DMRS, similarly to other subframes as illustrated in FIG.1 (for example, see NPL 6). The second method is a method (ratematching) of mapping data to 11 SC-FDMA symbols excluding the lastsymbol while changing the code rate for the data from other subframes asthe format of transmitting data in an SRS transmission candidatesubframe (for example, see NPL 7).

Both of the two methods described above presuppose the PUSCH subframeconfiguration of existing LTE as illustrated in FIG. 1 , or in otherwords, that the last symbol of a single subframe made up of 14 symbolsis always a data symbol.

Among the repetition methods described above, with repetition at theresource unit level (see FIG. 5 ) and repetition at the subframe level(see FIG. 6 ), the PUSCH subframe configuration of existing LTE may bemaintained, thereby making it possible to avoid collisions with the SRSof existing LTE due to puncturing the last symbol of a single subframeor rate matching. However, with the repetition at the resource unitlevel and repetition at the subframe level, the effects of symbol levelcombining may not be obtained sufficiently.

On the other hand, with repetition at the symbol level (see FIG. 7 ) inwhich the effects of symbol level combining are obtained sufficiently,the last symbol of a single subframe made up of 14 symbols is notnecessarily a data symbol. For example, in the example illustrated inFIG. 7 , the last symbol of the first and third subframes is the DMRS.Thus, in the case in which these subframes are SRS transmissioncandidate subframes, an NB-IoT terminal must puncture the DMRS mapped tothe last symbol similar to existing LTE. Note that since the DMRS is notcoded like the data, rate matching cannot be applied to the DMRS.

However, improvements in channel estimation accuracy are essential,particularly in environments where coverage enhancement is required, andit is desirable to avoid puncturing the DMRS. On the other hand, it isalso conceivable to set the SRS subframe on the base station side sothat the NB-IoT terminal avoids subframes that transmit the DMRS in thelast symbol, but this setting limits the operation of existing LTE.

Accordingly, one aspect of the present disclosure minimizes the effectof a collision (the DMRS being punctured in an SRS transmissioncandidate subframe) between the uplink transmission of an NB-IoTterminal that transmits repetitions at the symbol level and the SRStransmission of an existing LTE terminal in an environment thataccommodates the coexistence of LTE terminals and NB-IoT terminals. Withthis arrangement, by performing channel estimation and symbol levelcombining using a sufficient number of DMRS symbols in the demodulationof a signal from an NB-IoT terminal, the base station is able to improvethe channel estimation accuracy and the received signal quality.

Hereinafter, exemplary embodiments of the present disclosure will bedescribed in detail and with reference to the drawings.

[Overview of Communication System]

The communication system according to each embodiment of the presentdisclosure is provided with a base station 100 and a terminal 200. Theterminal 200 is an NB-IoT terminal, for example. Also, in thecommunication system, an environment is supposed in which NB-IoTterminals (the terminal 200) and existing LTE terminals coexist.

FIG. 8 is a block diagram illustrating the principal configuration ofthe terminal 200 according to each embodiment of the present disclosure.In the terminal 200 illustrated in FIG. 8 , a repetition unit 212repeats a data signal and the demodulation reference signal (DMRS) atthe symbol level over a plurality of subframes. A signal allocation unit213 maps, in the a plurality of subframes, the repeated DMRS to a symbolother than a symbol corresponding to an SRS resource candidate, which isa candidate for a resource to which the sounding reference signal (SRS)used to measure the uplink received signal quality is to be mapped. Atransmission unit 216 transmits the uplink signal (PUSCH) including theDMRS and the data signal in the a plurality of subframes.

Embodiment 1

[Base Station Configuration]

FIG. 9 is a block diagram illustrating a configuration of the basestation 100 according to Embodiment 1 of the present disclosure. In FIG.9 , the base station 100 includes a control unit 101, a control signalgeneration unit 102, a coding unit 103, a modulation unit 104, a signalallocation unit 105, an inverse fast Fourier transform (IFFT) unit 106,a cyclic prefix (CP) addition unit 107, a transmission unit 108, anantenna 109, a reception unit 110, a CP removal unit 111, a fast Fouriertransform (FFT) unit 112, a combining unit 113, a demapping unit 114, achannel estimation unit 115, an equalization unit 116, a demodulationunit 117, a decoding unit 118, and a determination unit 119.

The control unit 101 decides an SRS resource candidate group in a cellwhile accounting for the amounts of SRS resources needed by each of thea plurality of terminals (existing LTE terminals) existing in the cellcovered by the base station 100, and outputs information indicating thedecided SRS resource candidate group to the control signal generationunit 102 and the combining unit 113. The SRS resource candidate group isselected from the table illustrated in FIG. 2 , for example.

Also, the control unit 101 outputs, to the combining unit 113 and thedemapping unit 114, information related to the mapping of the DMRS anddata to SC-FDMA symbols when the NB-IoT terminal (the terminal 200)transmits by repetition.

In addition, the control unit 101 decides the allocation of the PUSCHwith respect to the NB-IoT terminal. At this time, the control unit 101decides the frequency allocation resources, the modulation/codingscheme, and the like to indicate to the NB-IoT terminal, and outputsinformation related to the decided parameters to the control signalgeneration unit 102.

Also, the control unit 101 decides the coding level for a controlsignal, and outputs the decided coding level to the coding unit 103.Also, the control unit 101 decides the radio resources (downlinkresources) that the control signal is to be mapped to, and outputsinformation related to the decided radio resources to the signalallocation unit 105.

In addition, the control unit 101 decides a coverage enhancement levelof the NB-IoT terminal, and outputs information related to the decidedcoverage enhancement level, or a repetition count required for PUSCHtransmission at the decided coverage enhancement level, to the controlsignal generation unit 102. Also, the control unit 101 generatesinformation related to the number of subcarriers to be used for PUSCHtransmission by the NB-IoT terminal, and outputs the generatedinformation to the control signal generation unit 102.

The control signal generation unit 102 generates a control signaldirected at the NB-IoT terminal. The control signal includes acell-specific higher-layer signal, a terminal-specific higher-layersignal, or an uplink grant indicating the allocation of the PUSCH.

The uplink grant contains a plurality of bits, and includes informationindicating frequency allocation resources, the modulation/coding scheme,and the like. Additionally, the uplink grant may also includeinformation related to a coverage enhancement level or a number ofrepetitions required for PUSCH transmission, and information related tothe number of subcarriers to be used for PUSCH transmission by theNB-IoT terminal.

The control signal generation unit 102 uses the control informationinput from the control unit 101 to generate a control information bitsequence, and outputs the generated control information bit sequence(control signal) to the coding unit 103. Note that since the controlinformation may also be transmitted to a plurality of NB-IoT terminals,the control signal generation unit 102 generates bit sequences thatinclude the terminal ID of each NB-IoT terminal in the controlinformation directed at each NB-IoT terminal. For example, cyclicredundancy check (CRC) bits masked by the terminal ID of the destinationterminal are added to the control information.

In addition, information about the SRS resource candidate group isreported to the NB-IoT terminal (a control unit 206 described later) bythe cell-specific higher-layer signaling. Information indicating thefrequency allocation resources and the modulation/coding scheme,information related to the coverage enhancement level or the number ofrepetitions required for PUSCH transmission, and information related tothe number of subcarriers to be used for PUSCH transmission by theNB-IoT terminal may also be reported to the NB-IoT terminal byterminal-specific higher-layer signaling, or by using the uplink grantindicating the allocation of the PUSCH as described above.

The coding unit 103, following the indicated coding level from thecontrol unit 101, codes the control signal (control information bitsequence) received from the control signal generation unit 102, andoutputs the coded control signal to the modulation unit 104.

The modulation unit 104 modulates the control signal received from thecoding unit 103, and outputs the modulated control signal (symbolsequence) to the signal allocation unit 105.

The signal allocation unit 105 maps the control signal (symbol sequence)received from the modulation unit 104 to the radio resources indicatedby the control unit 101. Note that the control channel on which thecontrol signal is to be mapped is the downlink control channel forNB-IoT. The signal allocation unit 105 outputs a downlink subframesignal, including the NB-IoT downlink control channel to which thecontrol signal is mapped, to the IFFT unit 106.

The IFFT unit 106 performs an IFFT process on the signal received fromthe signal allocation unit 105, thereby transforming a frequency-domainsignal to a time-domain signal. The IFFT unit 106 outputs thetime-domain signal to the CP addition unit 107.

The CP addition unit 107 adds a CP to the signal received from the IFFTunit 106, and outputs the signal with the added CP (an OFDM signal) tothe transmission unit 108.

The transmission unit 108 performs radio-frequency (RF) processing suchas digital-to-analog (D/A) conversion and upconversion on the OFDMsignal received from the CP addition unit 107, and transmits a radiosignal to the NB-IoT terminal (terminal 200) via the antenna 109.

The reception unit 110 performs RF processing such as downconversion andanalog-to-digital (A/D) conversion on an uplink signal (PUSCH) from theterminal 200 received via the antenna 109, and outputs the obtainedreceived signal to the CP removal unit 111. The uplink signal (PUSCH)transmitted from the terminal 200 includes a signal that is repeatedover a plurality of subframes.

The CP removal unit 111 removes the CP added to the received signalreceived from the reception unit 110, and outputs the signal with the CPremoved to the FFT unit 112.

The FFT unit 112 applies an FFT process to the signal received from theCP removal unit 111, decomposes the signal into a signal sequence in thefrequency domain, extracts the signals corresponding to the PUSCHsubframes, and outputs the extracted PUSCH signals to the combining unit113.

The combining unit 113 uses the information related to the SRS resourcecandidate group and information related to PUSCH repetition transmittedby the NB-IoT terminal (information related to the number of repetitionsand the mapping of the DMRS and data to SC-FDMA symbols when the NB-IoTtransmits by repetition) input from the control unit 101 to performsymbol level combining of the PUSCH transmitted by repetition over aplurality of subframes, and coherently combines the signals of theportion corresponding to the data signal and the DMRS.

The combining unit 113 outputs the combined signal to the demapping unit114.

The demapping unit 114 extracts the signal of the PUSCH subframe portionfrom the signal received from the combining unit 113. Subsequently, thedemapping unit 114 uses information related to the PUSCH repetitiontransmission by the NB-IoT terminal input from the control unit 101,decomposes the extracted signal of the PUSCH subframe portion intoSC-FDMA data symbols and the DMRS, and outputs the DMRS to the channelestimation unit 115, while outputting the SC-FDMA data symbols to theequalization unit 116.

The channel estimation unit 115 performs channel estimation using theDMRS input from the demapping unit 114. The channel estimation unit 115outputs the obtained channel estimation values to the equalization unit116.

The equalization unit 116 uses the channel estimation values input fromthe channel estimation unit 115 to perform equalization of the SC-FDMAdata symbols input from the demapping unit 114. The equalization unit116 outputs the equalized SC-FDMA data symbols to the demodulation unit117.

The demodulation unit 117 applies the inverse discrete Fourier transform(IDFT) to the frequency-domain SC-FDMA data symbols input from theequalization unit 116, and after transformation to a time-domain signal,performs data demodulation. Specifically, the demodulation unit 117converts a symbol sequence into a bit sequence on the basis of amodulation scheme indicated to the NB-IoT terminal, and outputs theobtained bit sequence to the decoding unit 118.

The decoding unit 118 performs error-correction decoding on the bitsequence input from the demodulation unit 117, and outputs the decodedbit sequence to the determination unit 119.

The determination unit 119 performs error detection on the bit sequenceinput from the decoding unit 118. The determination unit 119 performserror detection using the CRC bits added to the bit sequence. If thedetermination result of the CRC bits is error-free, the determinationunit 119 retrieves the received data, and reports an ACK to the controlunit 101. On the other hand, if the determination result of the CRC bitsreturns an error, the determination unit 119 reports a NACK to thecontrol unit 101.

[Terminal Configuration]

FIG. 10 is a block diagram illustrating a configuration of the terminal200 according to Embodiment 1 of the present disclosure. In FIG. 10 ,the terminal 200 includes an antenna 201, a reception unit 202, a CPremoval unit 203, an FFT unit 204, a control signal extraction unit 205,a control unit 206, a coding unit 207, a modulation unit 208, a DMRSgeneration unit 209, a multiplexing unit 210, a DFT unit 211, arepetition unit 212, a signal allocation unit 213, an IFFT unit 214, aCP addition unit 215, and a transmission unit 216.

The reception unit 202 receives the control signal (downlink controlchannel for NB-IoT) transmitted from the base station 100 via theantenna 201, performs RF processing such as downconversion and ADconversion on the received radio signal, and obtains a baseband OFDMsignal. The reception unit 202 outputs the OFDM signal to the CP removalunit 203.

The CP removal unit 203 removes the CP added to the OFDM signal receivedfrom the reception unit 202, and outputs the signal with the CP removedto the FFT unit 204.

The FFT unit 204 performs an FFT process on the signal received from theCP removal unit 203, thereby transforming a time-domain signal to afrequency-domain signal. The FFT unit 204 outputs the frequency-domainsignal to the control signal extraction unit 205.

The control signal extraction unit 205 performs blind decoding on thefrequency-domain signal (downlink control channel for NB-IoT) receivedfrom the FFT unit 204, and attempts to decode a control signal addressedto oneself. The control signal addressed to the terminal 200 includes anadded CRC masked by the terminal ID of the NB-IoT terminal.Consequently, if the CRC determination is OK as a result of the blinddecoding, the control signal extraction unit 205 extracts and outputsthe control information to the control unit 206.

The control unit 206 controls PUSCH transmission on the basis of thecontrol signal input from the control signal extraction unit 205.

Specifically, the control unit 206 indicates resource allocation forPUSCH transmission to the signal allocation unit 213 on the basis ofPUSCH resource allocation information included in the control signal.

Also, on the basis of information about the coding scheme and themodulation scheme included in the control signal, the control unit 206indicates the coding scheme and the modulation scheme for PUSCHtransmission to the coding unit 207 and the modulation unit 208,respectively. Also, in the case in which information related to acoverage enhancement level or information related to the number ofrepetitions required for PUSCH transmission is included in the controlsignal, on the basis of the information, the control unit 206 decidesthe number of repetitions for PUSCH repetition transmission, andindicates information expressing the decided number of repetitions tothe repetition unit 212. Also, in the case in which information relatedto the number of subcarriers to be used for PUSCH transmission by theNB-IoT terminal is included in the control signal, on the basis of theinformation, the control unit 206 indicates the number of subcarriersand the number X of subframes per resource unit for PUSCH transmissionto the signal allocation unit 213.

Also, in the case in which information related to the coverageenhancement level, information related to the number of repetitionsrequired for PUSCH transmission, or information related to the codingscheme and modulation scheme is reported from the base station 100 in ahigher layer, on the basis of the reported information, the control unit206 decides the number of repetitions for PUSCH repetition transmissionor the coding scheme and modulation scheme, and indicates the decidedinformation to the repetition unit 212, or to the coding unit 207 andthe modulation unit 208. Similarly, in the case in which informationrelated to the number of subcarriers to be used for PUSCH transmissionby the NB-IoT terminal is reported from the base station 100 in a higherlayer, on the basis of the reported information, the control unit 206indicates the number of subcarriers and the number X of subframes perresource unit for PUSCH transmission to the signal allocation unit 213.

Also, the control unit 206 outputs information related to the SRSresource candidate group reported from the base station 100 in acell-specific higher layer to the signal allocation unit 213.

Also, the control unit 206 outputs information related to the mapping ofthe DMRS and data to SC-FDMA symbols when the NB-IoT terminal transmitsby repetition to the multiplexing unit 210, the repetition unit 212, andthe signal allocation unit 213.

The coding unit 207 adds CRC bits masked by the terminal ID t the inputtransmission data, performs error-correction coding according to thecoding scheme indicated from the control unit 206, and outputs a codedbit sequence to the modulation unit 208.

The modulation unit 208 modulates the bit sequence received from thecoding unit 207 on the basis of the modulation scheme indicated from thecontrol unit 206, and outputs a modulated data symbol sequence to themultiplexing unit 210.

The DMRS generation unit 209 generates the DMRS, and outputs thegenerated DMRS to the multiplexing unit 210.

On the basis of the information related to the mapping of the DMRS anddata to SC-FDMA symbols input from the control unit 206, themultiplexing unit 210 multiplexes the data symbol sequence received fromthe modulation unit 208 and the DMRS received from the DMRS generationunit 209, and outputs a multiplexed signal to the DFT unit 211.

The DFT unit 211 applies the DFT to the signal input from themultiplexing unit 210 to generate and output a frequency-domain signalto the repetition unit 212.

In the case in which the local terminal is in a coverage enhancementmode, on the basis of the number of repetitions indicated from thecontrol unit 206, the repetition unit 212 repeats the signal input fromthe DFT unit 211 over a plurality of subframes, and generates arepetition signal. The repetition unit 212 outputs the repetition signalto the signal allocation unit 213.

The signal allocation unit 213 maps the signal received from therepetition unit 212 to PUSCH time/frequency resources allocated inaccordance with the indication from the control unit 206. Also, on thebasis of the information related to the SRS resource candidate groupreceived from the control unit 206, the signal allocation unit 213punctures the signal mapped to the symbols corresponding to the SRSresource candidates of the SRS transmission candidate subframes. Thesignal allocation unit 213 outputs the signal-mapped PUSCH signal to theIFFT unit 214.

The IFFT unit 214 performs an IFFT process on the frequency-domain PUSCHsignal input from the signal allocation unit 213, and thereby generatesa time-domain signal. The IFFT unit 214 outputs the generated signal tothe CP addition unit 215.

The CP addition unit 215 adds a CP to the time-domain signal receivedfrom the IFFT unit 214, and outputs the signal with the added CP to thetransmission unit 216.

The transmission unit 216 performs RF processing such as D/A conversionand upconversion on the signal received from the CP addition unit 215,and transmits a radio signal to the base station 100 via the antenna201.

[Operations of base station 100 and terminal 200] Operations in the basestation 100 and the terminal 200 having the above configurations will bedescribed in detail.

The base station 100 reports the srs-SubframeConfig to the terminal 200as a cell-specific higher-layer indication that sets the SRS resourcecandidate group. Also, communication is performed by having the basestation 100 allocate resource units inside the NB-IoT band to the NB-IoTterminal, namely the terminal 200.

In addition, the base station 100 decides the allocation of the PUSCHwith respect to the NB-IoT terminal. PUSCH allocation informationincludes frequency allocation resource information to indicate to theNB-IoT terminal, information related to the coding scheme and themodulation scheme, and the like. The PUSCH allocation information may bereported from the base station 100 to the terminal 200 through aterminal-specific higher layer, or by using the downlink control channelfor NB-IoT.

Also, before transmitting and receiving the PUSCH, the base station 100indicates the number of repetitions (R) to the NB-IoT terminal inadvance. The number of repetitions (R) may be indicated from the basestation 100 to the terminal 200 through a terminal-specific higherlayer, or by using the downlink control channel for NBIoT.

Also, before transmitting and receiving the PUSCH, the base station 100indicates the number of transmission subcarriers (for example, 1, 3, 6,or 12 subcarriers) to be used for PUSCH transmission by the NB-IoTterminal to the NB-IoT terminal in advance. The number of transmissionsubcarriers may be indicated from the base station 100 to the terminal200 through a terminal-specific higher layer, or by using the downlinkcontrol channel for NB-IoT.

The terminal 200 decides the number X of subframes per resource unit onthe basis of the indicated number of subcarriers. For example, in thecase in which the number of transmission subcarriers is 1, 3, 6, or 12,the terminal 200 decides the number of subframes per resource unit to beX=8, 4, 2, or 1, respectively.

Also, the terminal 200 transmits the PUSCH by repetition, for the numberof repetitions (R) reported from the base station 100. Consequently, theterminal 200 transmits the PUSCH over (X×R) subframes. For example, ifthe number of SC-FDMA symbols per subframe is the same 14 symbols asexisting LTE systems, in (X×R) subframes, (14×X×R) SC-FDMA symbols areincluded.

Also, the terminal 200 transmits the PUSCH using repetition at thesymbol level. At this time, the terminal 200 maps all DMRS included inthe repetition signal (PUSCH signal) consecutively from the beginningsymbol of the a plurality of subframes in which to perform the PUSCHrepetition. Specifically, the terminal 200 maps the DMRS consecutivelyover 2R symbols from the beginning of the subframes in which to performthe PUSCH repetition.

FIG. 11 illustrates how PUSCH repetition is performed in the case of X=1subframe and R=4 subframes.

As illustrated in FIG. 11 , one subframe includes two DMRS, and in the 4(=X×R) subframes in which the terminal 200 transmits by repetition, 8(=2R) DMRS are included. Accordingly, in FIG. 11 , the terminal 200 mapsthe DMRS consecutively (hereinafter also called DMRS repetition) over 8SC-FDMA symbols (=2R) from the beginning of the subframes in which toperform the PUSCH repetition (4-symbol repetition).

Note that in the case in which X>1 (not illustrated), it is sufficientfor the terminal 200 to perform the DMRS repetition of 2R symbols on acycle of R subframes.

Herein, in the case of 2R<14 (the number of SC-FDMA symbols persubframe), or in other words, in the case in which the number ofrepetitions R is less than (14/2)=7, in the terminal 200, the DMRS isnot mapped to the last symbol (the 14th symbol from the beginning) ofone subframe. In other words, the terminal 200 maps the DMRS to SC-FDMAsymbols other than the last symbol of a subframe (SRS transmissioncandidate subframe) in which an existing LTE terminal may possiblytransmit the SRS.

Also, the terminal 200 specifies the SRS transmission candidatesubframes on the basis of the srs-SubframeConfig indicated from the basestation 100. Additionally, in the SRS transmission candidate subframes,the terminal 200 punctures the last symbol of the 14 SC-FDMA symbols. Asdescribed above, the DMRS is not mapped to the last symbol of asubframe. In other words, a data symbol is always mapped to the lastsymbol of an SRS transmission candidate subframe. Thus, in the terminal200, in the last symbol of an SRS transmission candidate subframe, adata symbol rather than the DMRS is punctured.

In so doing, in the case in which the NB-IoT terminal, namely theterminal 200, performs PUSCH repetition at the symbol level, the DMRS ismapped to SC-FDMA symbols other than the SC-FDMA symbol (the last symbolof an SRS transmission candidate subframe) corresponding to an SRSresource candidate in which an LTE terminal may possibly transmit theSRS.

On the other hand, the base station 100 demodulates the data signalusing the DMRS included in the PUSCH transmitted from the terminal 200.As described above, even in the case in which SRS transmission candidatesubframes are included among the subframes in which PUSCH repetition isperformed by the NB-IoT terminal, the DMRS is not punctured in theNB-IoT terminal. Thus, the base station 100 is able to perform channelestimation and symbol level combining using a sufficient number of DMRSsymbols for the received PUSCH.

Also, in FIG. 11 , since all DMRS symbols are mapped consecutively fromthe beginning symbol of the a plurality of subframes in which the PUSCHrepetition is performed, compared to the case of simply expanding themapping of the data signal and the DMRS of an existing LTE system (FIG.7 ), the base station 100 is able to perform symbol level combiningusing twice as many DMRS. Thus, according to the present embodiment, thebase station 100 is able to improve the channel estimation accuracy.

Also, since a known signal, namely the DMRS, is mapped consecutively atthe beginning of the subframes in which the PUSCH repetition isperformed, the base station 100 is able to perform frequency errorestimation and timing detection accurately.

Also, as described above, by controlling the mapping of the DMRS in theNB-IoT terminal, the puncturing of the DMRS is avoided. In other words,according to the present embodiment, in the base station 100, it is notnecessary to change the SRS subframe settings with respect to theexisting LTE system.

According to the above, in the present embodiment, it is possible toimprove the transmission quality for NB-IoT terminals while minimizingthe impact on an existing LTE system.

Embodiment 2

Embodiment 1 describes a method of avoiding collisions between the SRStransmission of an existing LTE terminal and the DMRS transmission of anNB-IoT terminal in the case in which the number of repetitions R<7. Incontrast, the present embodiment describes a method of avoidingcollisions between the SRS transmission of an existing LTE terminal andthe DMRS transmission of an NB-IoT terminal even in the case in whichthe number of repetitions R≥7. In other words, the present embodimentdescribes a method in which the DMRS is not mapped to the last symbol ofa subframe, regardless of the value of the number of repetitions R.

Note that the base station and the terminal according to the presentembodiment share the basic configurations of the base station 100 andthe terminal 200 according to Embodiment 1, and thus will be describedby citing FIGS. 9 and 10 .

The base station 100 indicates the srs-SubframeConfig to the terminal200 as a cell-specific higher-layer indication that sets the SRSresource candidate group. Also, communication is performed by having thebase station 100 allocate resource units inside the NB-IoT band to theNB-IoT terminal, namely the terminal 200.

In addition, the base station 100 decides the allocation of the PUSCHwith respect to the NB-IoT terminal. PUSCH allocation informationincludes frequency allocation resource information to indicate to theNB-IoT terminal, information related to the coding scheme and themodulation scheme, and the like. The PUSCH allocation information may beindicated from the base station 100 to the terminal 200 through aterminal-specific higher layer, or by using the downlink control channelfor NB-IoT.

Also, before transmitting and receiving the PUSCH, the base station 100indicates the number of repetitions (R) to the NB-IoT terminal inadvance. The number of repetitions (R) may be indicated from the basestation 100 to the terminal 200 through a terminal-specific higherlayer, or by using the downlink control channel for NBIoT.

Also, before transmitting and receiving the PUSCH, the base station 100indicates the number of transmission subcarriers (for example, 1, 3, 6,or 12 subcarriers) to be used for PUSCH transmission by the NB-IoTterminal to the NB-IoT terminal in advance. The number of transmissionsubcarriers may be indicated from the base station 100 to the terminal200 through a terminal-specific higher layer, or by using the downlinkcontrol channel for NB-IoT.

Also, the base station 100 decides a number of DMRS partitions (N) or anumber of symbol repetitions (R′) that expresses the number of DMRSsymbols to transmit consecutively with respect to the NB-IoT terminal.The number of DMRS partitions (N) or the number of symbol repetitions(R′) may be indicated from the base station 100 to the terminal 200through a terminal-specific higher layer, or by using the downlinkcontrol channel for NB-IoT. Also, the number of DMRS partitions (N) orthe number of symbol repetitions (R′) may be predefined parametersstipulated by a standard.

The terminal 200 decides the number X of subframes per resource unit onthe basis of the indicated number of subcarriers. For example, in thecase in which the number of transmission subcarriers is 1, 3, 6, or 12,the terminal 200 decides the number of subframes per resource unit to beX=8, 4, 2, or 1, respectively.

Also, the terminal 200 transmits the PUSCH by repetition, for the numberof repetitions (R) indicated from the base station 100. Consequently,the terminal 200 transmits the PUSCH over (X×R) subframes. For example,if the number of SC-FDMA symbols per subframe is the same 14 symbols asexisting LTE systems, in (X×R) subframes, (14×X×R) SC-FDMA symbols areincluded.

Also, the terminal 200 transmits the PUSCH using repetition at thesymbol level. At this time, the terminal 200 maps the a plurality ofDMRS included in the repetition signal (PUSCH signal) distributed everycertain number (R′) of consecutive symbols (divided into N groups).Specifically, the terminal 200 performs the consecutive DMRS mapping(DMRS repetition) of (2R/N) symbols on a period of R/N subframes fromthe beginning of the a plurality of subframes in which to perform thePUSCH repetition.

For example, the terminal 200 maps the DMRS consecutively over (2R/N)symbols from the beginning symbol of the a plurality of subframes inwhich to perform the PUSCH repetition, and thereafter maps the DMRS over(2R/N) symbols on a period of (R/N) subframes. In other words, theterminal 200 maps the DMRS consecutively over R′ symbols at thebeginning of the PUSCH repetition subframes, and thereafter maps theDMRS over R′ symbols on a period of (R′/2) subframes.

FIG. 12 illustrates how PUSCH repetition is performed in the case of X=1subframe, R=4 subframes, and N=2 (or R′=4).

As illustrated in FIG. 12 , one subframe includes two DMRS, and in the 4(=X×R) subframes in which the terminal 200 transmits by repetition, 8(=2R) DMRS are included.

In FIG. 12 , the terminal 200 maps the DMRS consecutively over 4 symbols(=2R/N or =R′) from the beginning of the subframes in which to performthe PUSCH repetition (4 symbol repetition). Furthermore, the terminal200 maps the DMRS consecutively over 4 symbols from the beginning of the3rd subframe after 2 subframes (=R/N or R′/2) from the beginningsubframe in which to perform the PUSCH repetition.

Herein, in the case in which N>R/7 or R′<14, in the terminal 200, theDMRS is not mapped to the last symbol of a subframe. In other words, theterminal 200 maps the DMRS to SC-FDMA symbols other than the last symbolof a subframe (SRS transmission candidate subframe) in which an existingLTE terminal may possibly transmit the SRS.

Also, the terminal 200 specifies the SRS transmission candidatesubframes on the basis of the srs-SubframeConfig indicated from the basestation 100. Additionally, in the SRS transmission candidate subframes,the terminal 200 punctures the last symbol of the 14 SC-FDMA symbols. Asdescribed above, the DMRS is not mapped to the last symbol of asubframe. In other words, a data symbol is always mapped to the lastsymbol of an SRS transmission candidate subframe. Thus, in the terminal200, in the last symbol of an SRS transmission candidate subframe, adata symbol rather than the DMRS is punctured.

In so doing, in the case in which the NB-IoT terminal, namely theterminal 200, performs PUSCH repetition at the symbol level, similarlyto Embodiment 1, the DMRS is mapped to SC-FDMA symbols other than theSC-FDMA symbol (the last symbol of an SRS transmission candidatesubframe) corresponding to an SRS resource candidate in which an LTEterminal may possibly transmit the SRS.

On the other hand, the base station 100 demodulates the data signalusing the DMRS included in the PUSCH transmitted from the terminal 200.As described above, even in the case in which SRS transmission candidatesubframes are included among the subframes in which PUSCH repetition isperformed by the NB-IoT terminal, the DMRS is not punctured in theNB-IoT terminal. Thus, the base station 100 is able to perform channelestimation and symbol level combining using a sufficient number of DMRSsymbols for the received PUSCH.

Also, in FIG. 12 , since a certain number (R′) of DMRS symbols aremapped consecutively, by appropriately setting the number of partitionsN or the number of repetitions R′, an improvement in the received signalpower of the DMRS by symbol level combining is obtained.

Also, in the present embodiment, as illustrated in FIG. 12 , since theDMRS is distributed in the time domain, it becomes possible to trackchannel fluctuations and compensate for frequency error. Thus, accordingto the present embodiment, the channel estimation accuracy may beimproved.

Also, in FIG. 12 , since a known signal, namely the DMRS, is mappedconsecutively at the beginning of the signal in which the PUSCHrepetition is performed, the base station 100 is able to performfrequency error estimation and timing detection accurately.

Also, as described above, by controlling the mapping of the DMRS in theNB-IoT terminal, the puncturing of the DMRS is avoided. In other words,according to the present embodiment, in the base station 100, it is notnecessary to change the SRS subframe settings with respect to theexisting LTE system.

According to the above, in the present embodiment, it is possible toimprove the transmission quality for NB-IoT terminals while minimizingthe impact on an existing LTE system.

Note that although the present embodiment describes the case of startingthe DMRS repetition from the beginning of the PUSCH repetition as oneexample, the start position of the DMRS repetition is not limited to thebeginning of the PUSCH repetition. For example, the terminal 200 mayalso add an offset in subframe units or slot units to the start positionof the DMRS repetition.

Even in the case of adding an offset in subframe units to the startposition of the DMRS repetition, if N<R/7 or R′<14, similarly to FIG. 12, the DMRS is not mapped to the last symbol of a subframe.

Also, in the case of adding an offset in slot units (let A be the offsetvalue) to the start position of the DMRS repetition, if N>2R/(14−Δ) orR′<14−Δ, the DMRS is not mapped to the last symbol of a subframe.

Embodiment 3

Embodiments 1 and 2 anticipate a case in which the NB-IoT terminalpunctures the last symbol of the 14 SC-FDMA symbols in the SRStransmission candidate subframes. In this case, provided that X is thenumber of subframes per resource unit, and R is the number ofrepetitions, the NB-IoT terminal transmits the PUSCH over (X×R)subframes, regardless of whether or not a subframe is an SRStransmission candidate subframe or the number of SRS transmissioncandidate subframes in the PUSCH transmission segment.

In other words, the transmission time required for the PUSCH repetitionis fixed. However, in Embodiments 1 and 2, although the puncturing ofthe DMRS symbols is avoided, data symbols are punctured. Thus, there isa possibility that degradation of signal characteristics may occur dueto the loss of data symbols, particularly in the case of a small numberof repetitions.

Accordingly, the present embodiment describes a method of preventingDMRS symbols and data symbols from being punctured in the SRStransmission candidate subframes by allowing the transmission timerequired for the PUSCH repetition to be different depending on whetheror not a subframe is an SRS transmission candidate subframe or thenumber of SRS transmission candidate subframes in the PUSCH transmissionsegment.

The base station and the terminal according to the present embodimentshare the basic configurations of the base station 100 and the terminal200 according to Embodiment 1, and thus will be described by citingFIGS. 9 and 10 .

The base station 100 indicates the srs-SubframeConfig to the terminal200 as a cell-specific higher-layer indication that sets the SRSresource candidate group. Also, communication is performed by having thebase station 100 allocate resource units inside the NB-IoT band to theNB-IoT terminal, namely the terminal 200.

In addition, the base station 100 decides the allocation of the PUSCHwith respect to the NB-IoT terminal. PUSCH allocation informationincludes frequency allocation resource information to indicate to theNB-IoT terminal, information related to the coding scheme and themodulation scheme, and the like. The PUSCH allocation information may beindicated from the base station 100 to the terminal 200 through aterminal-specific higher layer, or by using the downlink control channelfor NB-IoT.

Also, before transmitting and receiving the PUSCH, the base station 100indicates the number of repetitions (R) to the NB-IoT terminal inadvance. The number of repetitions (R) may be indicated from the basestation 100 to the terminal 200 through a terminal-specific higherlayer, or by using the downlink control channel for NBIoT.

Also, before transmitting and receiving the PUSCH, the base station 100indicates the number of transmission subcarriers (for example, 1, 3, 6,or 12 subcarriers) to be used for PUSCH transmission by the NB-IoTterminal to the NB-IoT terminal in advance. The number of transmissionsubcarriers may be indicated from the base station 100 to the terminal200 through a terminal-specific higher layer, or by using the downlinkcontrol channel for NB-IoT.

The terminal 200 decides the number X of subframes per resource unit onthe basis of the indicated number of subcarriers. For example, in thecase in which the number of transmission subcarriers is 1, 3, 6, or 12,the terminal 200 decides the number of subframes per resource unit to beX=8, 4, 2, or 1, respectively.

Also, the terminal 200 specifies the SRS transmission candidatesubframes on the basis of the srs-SubframeConfig indicated from the basestation 100.

Also, the terminal 200 transmits the PUSCH by repetition, for the numberof repetitions (R) indicated from the base station 100. At this time,the terminal 200 transmits the PUSCH using repetition at the symbollevel. During the PUSCH repetition transmission, the terminal 200 doesnot map the DMRS and the data symbols to the last symbol correspondingto an SRS resource candidate among the 14 SC-FDMA symbols in the SRStransmission candidate subframes. In other words, the terminal 200 mapsthe DMRS and data symbols to symbols other than the last symbol of the14 SC-FDMA symbols in the SRS transmission candidate subframes.

In other words, the terminal 200 delays the transmission of the PUSCHsignal after the last symbol of an SRS transmission candidate subframe,with the amount of delay being equal to the last symbol (the amount bywhich the PUSCH signal is not mapped).

In this way, the terminal 200, does not transmit a signal (DMRS or data)in the last symbol of an SRS transmission candidate subframe. In otherwords, the terminal 200 does not puncture any of the DMRS signals ordata symbols.

FIG. 13 illustrates how PUSCH repetition is performed in the case of X=1subframe and R=4 subframes. Also, in FIG. 13 , srs-SubframeConfig=0, orin other words, the SRS transmission candidate subframes exist on a 1 msperiod (see FIG. 2 ).

As illustrated in FIG. 13 , the terminal 200 performs symbol levelrepetition of each SC-FDMA symbol included in one resource unit (X=1).In other words, similarly to FIG. 7 , the terminal 200 consecutivelymaps SC-FDMA symbols including the same signals (DMRS symbols and datasymbols).

However, the terminal 200 does not transmit a signal in the last symbol(the symbol corresponding to an SRS resource candidate) in SRStransmission candidate subframes, and instead delays by one symbol theSC-FDMA symbols to be transmitted after the SC-FDMA symbol.

With this arrangement, as illustrated in FIG. 13 , in the terminal 200,the DMRS and data symbols are not mapped to the last symbol of asubframe. In other words, the terminal 200 does not transmit the DMRSand data symbols in the last symbol of a subframe (SRS transmissioncandidate subframe) in which an existing LTE terminal may possiblytransmit the SRS. In other words, the terminal 200 does not puncture theDMRS and data symbols in the SRS transmission candidate subframes.

Note that, provided that N_(SRS) is the number of SRS transmissioncandidate subframes in the PUSCH repetition, the terminal 200 performsthe PUSCH repetition transmission using (14×X×R+N_(SRS)) SC-FDMAsymbols. In other words, the terminal 200 performs the PUSCH repetitiontransmission using ceiling((14×X×R+N_(SRS))/14) subframes. Herein, thefunction ceiling(X) expresses a ceiling function that returns thesmallest integer equal to or greater than x. For example, in FIG. 13 ,since X=1, R=4, and N_(SRS)=4, in the PUSCH repetition transmission, adelay of 4 SC-FDMA symbols occurs, and 5 subframes are used.

In so doing, in the case in which the NB-IoT terminal, namely theterminal 200, performs PUSCH repetition at the symbol level, similarlyto Embodiment 1, the DMRS and the data signal are mapped to SC-FDMAsymbols other than the SC-FDMA symbol (the last symbol of an SRStransmission candidate subframe) corresponding to an SRS resourcecandidate in which an LTE terminal may possibly transmit the SRS.

On the other hand, the base station 100 demodulates the data signalusing the DMRS included in the PUSCH transmitted from the terminal 200.As described above, in the case in which SRS transmission candidatesubframes are included among the subframes in which PUSCH repetition isperformed by the NB-IoT terminal, the base station 100 judges that thesignal from the NB-IoT terminal is not mapped to the last symbol of anSRS transmission candidate subframe, and is being transmitted with a1-symbol delay.

With this arrangement, loss due to puncturing in the terminal 200 may beavoided for not only the DMRS but also data symbols. Thus, in thepresent embodiment, the base station 100 is able to improve the channelestimation and the received signal quality for the received PUSCH. Thus,in the present embodiment, it is possible to improve the transmissionquality for NB-IoT terminals while minimizing the impact on an existingLTE system.

Note that in the present embodiment, the method of mapping data and theDMRS to SC-FDMA symbols is arbitrary. Also, in the present embodiment,unlike Embodiment 1 or 2, since data symbols are also not punctured, thereceived signal quality at the base station 100 does not depend on thenumber of SRS transmission candidate subframes.

The above thus describes exemplary embodiments of the presentdisclosure.

Note that the values of the number of repetitions, the value of theparameter X, the number of partitions (N), the number of symbolrepetitions (R′), and the values of the parameters defined in thesrs-SubframeConfig are merely examples, and are not limited to theabove.

Also, although the foregoing embodiments are described by taking thecase of configuring an aspect of the present disclosure by hardware asan example, it is also possible to realize the present disclosure bysoftware in conjunction with hardware.

In addition, each function block used in the description of theforegoing embodiments typically is realized as an integrated circuit,that is, an LSI chip. The integrated circuit controls each functionblock used in the description of the foregoing embodiments, and may beprovided with inputs and outputs. The function blocks may be realizedindividually as separate chips, or as a single chip that includes someor all function blocks. Although LSI is discussed herein, the circuitintegration methodology may also be referred to as IC, system LSI, superLSI, or ultra LSI, depending on the degree of integration.

Furthermore, the circuit integration methodology is not limited to LSI,and may be also be realized with special-purpose circuits orgeneral-purpose processors. A field-programmable gate array (FPGA)capable of being programmed after fabrication of the LSI chip, or areconfigurable processor whose circuit cell connections and settingsinside the LSI chip may be reconfigured, may also be used.

Furthermore, if circuit integration technology that may be substitutedfor LSI appears as a result of progress in semiconductor technology oranother derived technology, obviously the new technology may be used tointegrate the function blocks. Biotechnology applications and the likeare also a possibility.

A terminal of the present disclosure adopts a configuration including: arepetition unit that performs a repetition for mapping a data signal anda demodulation reference signal (DMRS) repeatedly at a symbol level overa plurality of subframes; a signal allocation unit that maps, in the aplurality of subframes, the repeated DMRS to symbols other than symbolscorresponding to an SRS resource candidate, which is a candidate for aresource to which a sounding reference signal (SRS) used to measure anuplink received signal quality is to be mapped; and a transmission unitthat transmits an uplink signal including the DMRS and the data signalin the a plurality of subframes.

In a terminal of the present disclosure, the signal allocation unit mapsall of the DMRS included in the uplink signal consecutively from abeginning symbol of the a plurality of subframes, and punctures the datasignal mapped to symbols corresponding to the SRS resource candidate.

In a terminal of the present disclosure, the signal allocation unit mapsa plurality of DMRS included in the uplink signal distributed everycertain number of consecutive symbols, and punctures the data signalmapped to symbols corresponding to the SRS resource candidate.

In a terminal of the present disclosure, among the a plurality ofsubframes, the signal allocation unit maps the DMRS and the data signalto symbols other than symbols corresponding to the SRS resourcecandidate, and does not map the uplink signal to symbols correspondingto the SRS resource candidate.

A transmission method of the present disclosure includes: performing arepetition for mapping a data signal and a demodulation reference signal(DMRS) repeatedly at a symbol level over a plurality of subframes;mapping, in the a plurality of subframes, the repeated DMRS to symbolsother than symbols corresponding to an SRS resource candidate, which isa candidate for a resource to which a sounding reference signal (SRS)used to measure an uplink received signal quality is to be mapped; andtransmitting an uplink signal including the DMRS and the data signal inthe a plurality of subframes.

An aspect of the present disclosure is useful in a mobile communicationsystem.

REFERENCE SIGNS LIST

-   -   100 base station    -   200 terminal    -   101, 206 control unit    -   102 control signal generation unit    -   103, 207 coding unit    -   104, 208 modulation unit    -   105, 213 signal allocation unit    -   106, 214 IFFT unit    -   107, 215 CP addition unit    -   108, 216 transmission unit    -   109, 201 antenna    -   110, 202 reception unit    -   111, 203 CP removal unit    -   112, 204 FFT unit    -   113 combining unit    -   114 demapping unit    -   115 channel estimation unit    -   116 equalization unit    -   117 demodulation unit    -   118 decoding unit    -   119 determination unit    -   205 control signal extraction unit    -   209 DMRS generation unit    -   210 multiplexing unit    -   211 DFT unit    -   212 repetition unit

1. An integrated circuit, comprising: reception circuitry, which, inoperation, controls receiving control information indicating a number ofsymbols on which a Demodulation Reference Signal (DMRS) is to be mapped;and transmission circuitry, which, in operation, controls transmitting asignal in a multiple consecutive time units, each of the multipleconsecutive time units including multiple time slots; wherein the DMRSis mapped to each of multiple non-consecutive sets in the multipleconsecutive time units, a number of symbols in each of the multiplenon-consecutive sets being determined based on the control information,the number of symbols of each of the multiple non-consecutive sets isless than 14 symbols regardless of a number of the multiple consecutivetime units, the symbols of each of the multiple non-consecutive sets aresymbols other than sounding reference signal (SRS) symbol candidates,and a number of the multiple consecutive time units is different foreach of numbers of subcarriers to be mapped.
 2. The integrated circuitaccording to claim 1, wherein each of the multiple non-consecutive setsis periodically allocated in multiple consecutive time units.
 3. Theintegrated circuit according to claim 1, wherein the SRS symbolcandidates is transmitted via a higher layer signaling.
 4. Theintegrated circuit according to claim 1, wherein a number of themultiple consecutive time units is different for each of numbers ofsubcarriers to be mapped.
 5. The integrated circuit according to claim1, wherein the numbers of subcarriers include less than 12 subcarriers.6. The integrated circuit according to claim 1, wherein the signal isgenerated without assuming the SRS symbol candidates, and some of thesignal relating to the SRS symbol candidates is punctured beforetransmission.
 7. The integrated circuit according to claim 1, wherein atotal number of symbols in the multiple non-consecutive sets isdetermined based on a repetition number of a physical shared uplinkchannel (PUSCH) and a number of subframes per a resource unit.